Among semiconductor elements, a power module for supplying power has a relatively high amount of heat generation. Therefore, as a substrate on which this power module is mounted, for example, a power module substrate including: a ceramic substrate that is formed of AlN (aluminum nitride), Al2O3 (alumina), or Si3N4 (silicon nitride); a circuit layer in which a first metal plate is bonded to one surface of the ceramic substrate; and a metal layer in which a second metal plate is bonded to the other surface of the ceramic substrate is used.
In such a power module substrate, a semiconductor element such as a power element is mounted on the circuit layer through a solder material.
PTL 1 discloses a power module substrate in which an aluminum plate is used as the first metal plate (circuit layer) and the second metal plate (metal layer).
PTLs 2 and 3 disclose a power module substrate in which a copper plate is used as the first metal plate (circuit layer) and the second metal plate (metal layer), and the copper plate is bonded to a ceramic substrate with an active metal method using an Ag—Cu—Ti-based brazing material.